The present invention relates to the field of fiber optics. In particular, this invention relates to a method and system for providing the automatic pre-emption of data transmission when impairment is detected in an associated fiber optic link.
Internet traffic is growing at a rate of approximately 400% a year and it appears that this trend will continue for at least a couple of years. To keep pace with the traffic requirement, high speed, dense electrical and optic fiber links have been deployed.
Optical amplifiers are commonly used in networks including optic fibers to receive, amplify and transmit data signals and control signals in the form of a light beam from a first contact point to a second contact point. The light beam, which is generally produced by a Laser, released by such optical amplifiers typically does not raise safety concerns when the light beam is confined within the optic fiber. However, when light beam is no longer confined to the optic fiber, such as is the case when an optic fiber cut occurs, the intensity of the light bean, released by the optical amplifiers is usually significantly above the acceptable safety levels and may be hazardous.
As a result of the above, methods have been developed for automatically shutting off optical amplifiers when a fiber cut in an optic fiber is detected. A typical approach includes a downstream optical amplifier adapted to monitor an optic fiber carrying an incoming signal to detect a fiber cut. When a fiber cut is detected, the downstream optical amplifier sends a message to the upstream optical amplifier to which it is associated causing the upstream optical amplifier to shut-off all transmissions over the damaged fiber optic link.
A deficiency with methods of the type described above is that the massaging exchange between the upstream and downstream optical amplifiers is frequently complex and introduces a delay between the time a cut in the optic fiber is detected and the time the transmission over the damage optic fiber is pre-empted.
An additional deficiency of methods of the type described above is that in order to re-establish communication over a fiber optic link after a fiber cut has been detected, the optical amplifiers must be periodically turned on and off in order to monitor the state of the fiber optic link in order to detect when the fiber optic link is put back into operation. This results in complex and lengthy reconnection times for the network.
A common method used in the detection of fiber optic cuts is the use of optical reflectometer tools. By applying short laser pulses to a fiber optic link input, the properties of the fiber optic link can he determined on the basis of the light returned to that input by reflection or backscattering within the fiber optic link. Major flaws, such as a cut or pull, in the fiber optic link give rise to substantial reflections producing peaks in the return signal as a function of time. For more information about optical reflectometer tools, the reader is invited to consult U. S. Pat. No. 5,822,094, xe2x80x9cSelf-Stimulated Signal Detection in an Optical Transmission Systemxe2x80x9d, issued to O""Sullivan et al. on Oct. 13, 1998. The contents of this document are hereby incorporated by reference.
Consequently, there is a need in the industry for providing a method and system for automatically pre-empting data transmission over a damaged optic fiber that at least partially alleviates the problems associated with methods and systems of prior art designs.
In accordance with a broad aspect, the invention provides a method for detecting communication path impairment and a communication path impairment detection module for use in connection with a duplex optic communication link. The duplex optic communication link includes an outgoing communication path and an incoming communication path, where a data channel and an optical service channel characterize each communication path. The communication path impairment detection module includes first and second ports for coupling to the outgoing communication path and the incoming communication path respectively. The communication path impairment detection module also includes a processing un t responsive to impairment of the data channel and of the optical service channel in the incoming communication path to impair the data channel and the optical service channel in the outgoing communication path.
In a very specific example of implementation, a first optic fiber establishes the outgoing communication path and a second optic fiber establishes the incoming communication path.
In an alternative very specific example of implementation, a bi-directional optic fiber establishes the outgoing communication path as well as the incoming communication path.
For the purpose of this specification, the expression outgoing communication path is used to designate a communication path that carries outgoing data and control signals from a given communication path impairment detection module. For the purpose of this specification, the expression incoming communication path is used to designate a communication path that carries incoming data and control signals to a given communication path impairment detection module.
Advantageously, by correlating the detection of impairment of the data channel and impairment of the optical service channel carried over a same optic fiber to initiate the impairment of the data channel and impairment of the optical service channel in the outgoing communication path, an improved likelihood of correct impairment detection is obtained. In other words, if both the optical service channel and the data channel are impaired and are both carried by the same optic fiber, there is a high likelihood that the impairment is due to the optic fiber.
In a non-limiting example of implementation, the processing unit is adapted to detect impairment of the data channel and the optical service channel in the incoming communication path. The processing unit disables transmission over the data channel of the outgoing communication path and impairs the optical service channel when the impairment of the data channel and of the optical service channel in the incoming communication path is detected.
More specifically, when the impairment of the optical service channel in the incoming communication path is characterized by either one of a low light intensity and an absence of light, the processing unit is operative for impairing the optical service channel in the outgoing communication path by including the transmission of a control data element of a first type in the outgoing communication path. The control data element of the first type conveys an impairment status associated to the optical service channel in the incoming communication path.
When the impairment, of the optical service channel in the incoming communication path is characterized by a presence of a control data element conveying an impairment status associated to the optical service channel and the data channel in the outgoing communication path, the processing unit is operative for impairing the optical service channel in the outgoing communications path by transmitting a control data element of a second type over the optical service channel in the outgoing communication path. The control-data element of the second type conveys a non-impairment status associated to the optical service channel in the incoming communication path.
Continuing the specific example, the processing unit is also operative for re-establishing transmission over the data channel in an outgoing communication path that was previously impaired. Transmission is re-established ,when absence of either one of impairment of the data channel and impairment of the optical service channel in the incoming communication path is detected.
In a non-limiting example, the communication path impairment detection module is a part of an optical amplifier.
In accordance with another broad aspect, the invention provides a communication system including communication path impairment detection modules of the type described above.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.